Folly Mills Calcareous Wetland

Augusta County, Virginia

Robert Hunsucker and R. F. Mueller

Abstract

The Folly Mills wetland in Augusta County, Virginia originates from
artesian springs in an area of dolomitic limestone. The wetland is the site
of a number of state rare plants. These include such disjunct northern species
as Carex interior, C. prairea, Juncus brachycephalus,
J. nodosus, Menyanthes trifoliata, Spiranthes lucida,
Lysimachia quadriflora, Salix discolor, Filipendula rubra
and Veronica scutellata. Parnassia grandifolia and the moss
Philonotis muehlenbergii also occur here. The wetland is the only known
site in the state for Salix discolor and one of only two extant
populations of Menyanthes. It appears to be a true island refugium
dating to glacial times. The character of the spring water, a topographic
trap, presence of herbivores and other factors may affect continuing existence
of the community. The most important consideration in protecting this wetland
is preservation of its watershed and spring recharge area.

Introduction

Calcareous wetlands constitute a very restricted class of habitats in
the Central Appalchians and thus far have received little attention in the
literature (T. F. Wieboldt, personal communication, 1996). Perhaps the
best-known example of this community type in the Central Appalachians is the
Altona Marsh in Jefferson County, West Virginia (Hutton et al, 1968;
Strausbaugh and Core, 1978). Somewhat similar wetlands in Ohio have been
studied by Stuckey and Denny (1981), but these occur in the area of the most
recent glaciation. A nearby wetland at Stuarts Draft, Virginia, shares a
number of state rare species, including Buckbean (Menyanthes
trifoliata), with the Folly Mills wetland (The Nature Conservancy, Virginia
Chapter News, 1995). Another example, the Barns Chapel Swamp of Washington
County, Virginia (Ogle, 1989) has similar soil chemistry and shares at least 15
species with Folly Mills. However there are also many species not shared by
the two wetlands, perhaps in part as a result of their separation by the
eastern continental divide. Like these examples, the Folly Mills wetland is
notable for its rare and disjunct northern species, which number at least
ten.

In addition to the interest these rare plants in themselves afford, the
communities in which they occur pose questions regarding their origin,
persistence in time and relations to coexisting fauna both today and in earlier
times. If, as it appears, the disjunct northern species are ice-age relicts,
what are the conditions for continuing maintenance of the community? What was
and is the role of natural disturbances such as fire and herbivore grazing and
browsing? There is good evidence that a megafauna of large herbivores and
carnivores existed in the region during late glacial times, up to perhaps
11,000 years ago (Guilday, 1984). Given the scarcity of wetlands in this
unglaciated region, such places were likely magnets for both herbivores and
carnivores for the special foraging and wallowing opportunities provided. To a
degree the same should have been true of the Holocene Bison, Elk and other
animals that once populated the area before settlement by Europeans.
Presettlement conditions, which presumably favored the establishment and
persistence of these communities, would seem to be desirable for their
protection and management today.

Setting

The Folly Mills wetland is located on the floodplain of Folly Mills
Creek, a headwater branch of the South Fork of the Shenandoah River. A major
fork of the stream lies just to the southeast upstream. Bedrock in the area is
Ordovician Beekmantown dolomitic limestone with prominent chert beds (Rader,
1967). Local relief in the area is about 300 ft (90 meters) and the wetland
lies at 1590 ft (480 meters) asl. Approximately 4 acres (1.6 ha) in area, it
occupies an embayment in a linear ridge that rises 120 ft (37 meters) on the
northwest. This ridge consists of bluish gray dolomitic limestone which
exhibits some coarse crystals of dolomite. The ridge is capped by a massive
bed of chert which is partly exposed and partly covered by soil. The wetland is
bounded on the southeast by the natural levee of the stream. The main water
source of the wetland appears to be a large artesian spring that wells up
within it. The flow of this spring, which is distributed over a wide area, has
built up marly clay deposits that have elevated the surface a foot or more
above the floodplain behind the levee. It is possible that the embayment in
the hillside is also at least in part a result of rock dissolution by the
spring. Because Folly Mills Creek is subject to extensive flooding, the
wetland is occasionally inundated to depths of a meter or more and thus
receives nutrient-rich alluvial deposits as a result.

Table 1 summarizes the chemical characteristics of the wetland soils at depths
of 0-10 and 10-20 cm at locations on the southeast (FM1) and northwest (FM2)
sides. Organic matter is particularly high in the surface samples. pH ranges
from slightly acid to slightly alkaline. Ca and Mg are high in all samples,
while P, K and soluble salts are low. Fe and some trace elements appear to be
concentrated in the surface organic matter.

The forest on the surrounding hills ranges from young to mature. While it can
be classified Oak-Chestnut as a whole (Braun, 1950) it shows considerable
variation in type, depending on aspect, slope and proximity to given rock
types. Oaks and Hickories dominate on chert ridges and some deep soil areas as
northwest of the wetland. However, on slopes immediately above the wetland
mesic species such as Juglans nigra, Ulmus rubra, Celtis
occidentalis and Morus rubra are abundant. The herb flora in such
areas is rich and diverse and includes such species as Panax
quinquefolius and Hydrastis canadensis. Where carbonate rocks are
near the surface there is a community dominated by Quercus muehlenbergii
and Fraxinus americana. This Ash also borders the wetland on the
floodplain. A determination in soil above carbonate yielded a pH of 7.7 but
measurements above chert ranged from 6.0 at the surface to 5.1 a foot (30 cm)
below the surface. pH is also expected to be lower on chert talus and areas of
oak leaf concentrations. It is likely that run-off from such areas exerts some
influence on wetland chemistry, and it is possible that the significantly lower
pH value of sample FM2 from the forest side of the wetland,relative to that of
FM1 on the steam side, reflects this influence.

Although local relief is not great, the topography of the Folly Mills Valley
has significant features that bear on the wetland microclimate. The Valley
upstream rises to 2200 ft (670 meters) asl at the headwater divide five miles
(8 km) to the southwest. Less than 1/4 mile (400 meters) below it is
constrained to a width of less than 100 feet (30 meters) and forms a bottleneck
for both water and cold air draining from up valley. One consequence is that
killing frosts have been recorded near the wetland as late as June 8.

Destructive farming practices gullied the hills and contributed subsoil
sediment to the floodplain and wetland. About 40 years ago an attempt was made
to drain the wetland by ditching to the stream and these ditches as well as the
material removed from them are still clearly recognizable. However there was
apparently little effect on the wetland due to the high volume of spring water
flow. This flow is remarkably constant with little apparent diminution during
even the driest weather of the last twenty years.

Total of 121 species of mosses, fern, spikemoss and flowering
plants:
8 spp of bryophytes
114 species of vascular plants: ferns 1, Spikemoss 1, flowering plants 108
12 out of 121 species are of special concern, rare etc.; 1 moss, 11 flowering
plant species
7 of the flowering plant species are not native (introduced from
Europe)

Plant Distribution in the Wetland

The wetland consists of two major parts, a central cattail marsh and
a sedge-forb meadow that surrounds the marsh. Species other than cattails that
are concentrated in the marsh are Peltandra virginica, Impatiens
capensis, Lemna valdiviana, Pilea pumila, Caltha
palustris and Menyanthes trifoliata. Menyanthes also extends
into the meadow. During the dormant season the location of the Buckbean in the
marsh is clearly visible on ærial photos since there are fewer cattails
where Buckbean occurs.

Virtually all plants other than those listed above are greatly concentrated in
the sedge-forb meadow. Some of the largest Pussy Willows, which range up to 15
ft (4.6 meters) high, are located on the northwest edge of the wetland and
almost merge with the upland forest. However other lower shrubs of this and
other willows are scattered in both meadows and marsh.

Although Caltha palustris, like Buckbean, is concentrated in the marsh,
it is largely separated from the latter and confined to the northeast end.

Filipendula rubra occurs mostly where the marsh and meadow meet and not
far from the upland forest edge on the northwest side of the marsh. Although
of very limited occurrence, Parnassia grandifolia is to some extent
associated with willow clumps in the meadow.

Discussion

The majority of plants of the Folly Mills Wetland have wide
distributions ranging from southern Canada southward. However there is also a
remarkable concentration of state-rare disjunct species that are either
confined to a region almost entirely north of Virginia or range into the Arctic
or sub-Arctic. A number of species , while not rare, also have markedly
northern distributions. Some of these, as well as a few of the rarer species,
have circumpolar or Eurasian ranges. By contrast, characteristically southern
species are few here, and only one state-rare species is in this category.
Among the state-rare northern species are Carex prairea,C.
interior, Juncus brachycephalus, J. nodosus, Menyanthes
trifoliata, Spiranthes lucida, Salix discolor , Veronica
scutellata and Filipendula rubra. Salix discolor is the
rarest of these since, as far as is known, it is confined to this site in
Virginia (Ludwig, personal communication, 1996). Parnassia grandifolia
is also regarded as very rare to uncommon (Ludwig, 1991). This species is
uncommon throughout its range which includes the Southern Appalachians and the
Ozarks, with Southern outliers in Florida and Texas. It is verified from ten
sites in Virginia at present (Ludwig, personal communication, 1996).

More common species with northern distributions are Campanula
aparinoides, Spiranthes cernua, Caltha palustris, Salix
eriocephala, Ranunculus carolinianus, Lycopus uniflorus,
Bidens frondosa, B. cernua and Mentha arvensis as well as
others less closely correlated.

Of the more common species in the state, but with a southern distribution,
Agalinis purpurea is very conspicuous in the meadow, while Peltandra
virginica is rare at Folly Mills.

In seeking answers to questions posed by the wetland community, attention was
drawn to the local setting in terms of geology, topography, ambient chemistry
and ice-age influences. Central here is the necessity of satisfying the
requirements of the disjunct northern flora as well as that of more southern
distribution. Ogle (1982) discussed the formation of "frost pockets" by a
combination of topographic features and the common influx of continental polar
air masses on the Blue Ridge plateau of Carroll and Grayson Counties in
Virginia. His interest was to explain the presence of northern species such as
Dalibarda repens and Vaccinium macrocarpon in a number of
dominantly acidic glades. These glades are 1000 ft (300 meters) or more higher
in elevation than the Folly Mills wetland, although at slightly lower latitude.
However the elevated upper watershed and topographic dam at Folly Mills might
well be as effective in trapping cold air as the glades. Like streams in the
vicinity of the glades, Folly Mills is a northeast-flowing stream, and thus, as
suggested by Ogle, is on the receiving end of polar air masses. In any case
late-season frost here is a matter of record. It is also likely that the
constant influx of cool Calcareous spring water creates salubrious conditions
for a variety of plants, including both northern and southern species at Folly
Mills (Mueller, 1994). In contrast to the Wetland the adjacent upland forest
contains few if any markedly northern species, with the possible exception of
Chimaphila umbellata (which occurs with C. maculata) and the
uncommon fruticose lichen Cetraria arenaria. However C.
umbellata also occurs on the North Carolina piedmont and coastal plain
(Radford et al, 1964) and C. arenaria occupies an unusual habitat under
Pinus virginiana here. The Southern Appalachian character of this
forest is further emphasized by the presence of Quercus stellata and
Diospyros virginiana. The wetland appears to be a true relictual
refugium.

Once the questions of stability with regard to topography and ambient
conditions are resolved there still remains the role of disturbances such as
fire and animal impacts. At present the wetland seems stable with respect to
both water flows and encroaching woody or other invasive vegetation. The
growth of certain of the rare species such as Buckbean is extraordinarily
vigorous and this plant may even be expanding its area of occupation. This may
in part be a conseqence of it being less palatable to the horses, which are at
present the dominant large herbivores. Indeed, the general stability of the
vegetation may be a result of the continuous presence of herbivores both in
presettlement and post-settlement times. As suggested earlier these
considerations should enter into any management plan for this community.

The Folly Mills community is of course vulnerable to a variety of threats to
its existence. Beyond management considerations looms possible impending
development of its watershed and spring recharge area, which could sap its
water supply and introduce degrading chemicals such as herbicides. There is
evidence that human impacts have already extirpated many rare plants in the
Central Appalachians. An example is the apparent disappearance of Buckbean
from certain previously known stations such as the Cranesville Swamp of West
Virginia (McDonald, 1993) and Big Meadows in Shenandoah National Park. The
continued existence of this wetland is dependent on protection of the watershed
that maintains the special hydrologic, climatic and perhaps unknown ecologic
conditions.

FM1

FM2

0-10cm

10-20cm

0-10cm

10-20cm

pH

7.7

7.6

6.6

7.2

OM%

6.0

2.9

5.5

2.1

SS

128.0

51.0

166.0

26.0

P

2.5

3.0

1.0

1.0

K

12.5

6.5

4.5

11.0

Ca

1200.0

1200.0

1200.0

648.0

Mg

120.0

120.0

120.0

120.0

Zn

6.1

1.7

5.3

0.6

Mn

16.1

16.1

10.9

4.9

Cu

21.3

1.7

11.9

0.6

Fe

833.3

709.1

108.1

83.3

Be

0.4

0.3

0.5

0.2

Table 1: Chemical analyses of the Folly Mills Wetland soils at two
sites and depths.
OM=organic matter in percent. Soluable Salts (SS) and all elements
are in parts per million. Analyses by Virginia Cooperative Extension Service
at Virginia Polytechnic and State University.

Acknowledgments

The investigators are indebted to the following individuals and
organization: Elizabeth DeMar Mueller, co-owner of the wetland, for unflagging
appreciation of its value and need for protection; Douglas Ogle for his many
suggestions and aid in bringing this work to publication; J. Christopher
Ludwig for his helpful comments; Gus Mueller for his observations, able word
processing and assistance with the manuscript. Dorothy Simpkims for continuous
support and Doris True and the Virginia Native Plant Society for their
interest, publicity and registration of this rare community.